The Associated Press projected Tuesday evening that Barrett had won the Democratic nomination over rival Kathleen Falk, a who had enjoyed the support of organized labor and the state's progressives.

Barrett's victory sets off a June 5 election versus Walker, a national Republican figure since his controversial effort to overhaul Wisconsin's collective bargaining laws for public employees shortly after assuming office in 2011.

The contest will mean a rematch between Walker and Barrett; they fought each other in the 2010 general election, and Walker won the governorship with just above 52 percent of the vote.

A Marquette University Law School poll last week pegged the early June recall election as a veritable dead heat between Barrett and Walker.